Congenital heart block (CHB) develops in 1-2% of anti-Ro/SSA-positive pregnancies and has a recurrence rate of 12-20%, which indicates that factors other than maternal autoantibodies are crucial for CHB to occur. Here, we aimed to evaluate the influence of factors previously associated with CHB on the occurrence of milder forms of fetal cardiac conduction disturbances, shown to occur in up to 30% of anti-Ro/SSA-positive pregnancies, and on neonatal outcome in a large cohort of prospectively followed pregnancies. The association of maternal age, season of the year and history of atrioventricular block (AVB) with the development of fetal Doppler and neonatal ECG conduction disturbances was evaluated in 212 anti-Ro52/SSA-positive singleton pregnancies. Maternal age was significantly higher in AVB II-III pregnancies but was not correlated with fetal AV time intervals in fetuses without signs of AVB II-III. AV time intervals of fetuses surveilled during the winter were significantly longer than those of fetuses surveilled during the summer. Fetal AV time intervals in consecutive pregnancies from the same women were significantly correlated. A history of AVB II-III was associated with significantly longer AV time intervals, and AVB I-III was observed at birth in 38% of babies born after a sibling with abnormal fetal AV conduction. Our study shows that AV time intervals in anti-Ro/SSA antibody-exposed fetuses during the CHB risk period are influenced by the season of the year, and reveals that the recurrence of conduction disturbances in antibody-exposed fetuses is higher than previously reported when milder forms are taken into account.